SEOUL, South Korea — President Moon Jae-in’s governing party in South Korea won a landslide in parliamentary elections Wednesday, as he leveraged his surging popularity over his country’s largely successful battle against the coronavirus to increase his political sway.​

With more than 99 percent of the votes counted, Moon’s ​left-leaning ​Democratic Party had won 163 seats in the 300-member National Assembly, according to the National Election Commission on Thursday morning. A satellite party the Democrats created for Wednesday’s elections won 17 seats. Together, the 2 groups took three-fifths of all seats, giving Moon the largest majority of seats in three decades.

The main conservative opposition United Future Party and its own satellite Future Korea Party suffered a crushing defeat, winning ​103 seats​ between them​. ​The remaining seats were taken by independents and candidates from smaller parties.

Pandemic or not, South Koreans proved eager to vote in the election, widely seen as a midterm referendum on Moon​, elected to a 5-year term in 2017.​ The voter turnout was 66.2 percent, the highest for a parliamentary election in 28 years.

Wednesday’s election marked the first time in 16 years that left-leaning parties ​have secured a parliamentary majority, as South Koreans expressed their support for Moon’s government, which has won plaudits for bringing the epidemic under control​. ​

Their victories could embolden Moon to reinvigorate his stalled diplomacy with North Korea and ​press ahead with domestic priorities, like reform​ing state prosecutors’ offices.

In South Korea, elections typically have been decided by regional loyalties​, ideological differences over North Korea or issues like the economy and corruption. But this time, “how the government has responded to the coronavirus was the most decisive factor in the president’s approval ratings and in the parliamentary ​election,” said Park Si-young, head of WinG Korea, a Seoul-based political survey company.

​The election in South Korea “tells other world leaders that how they respond to their own crisis could make or break their political fortunes,” said Duyeon Kim, a senior adviser on Northeast Asia and nuclear policy at the International Crisis Group. “Because the pandemic is at the top of everyone’s mind.”